C# 功能区组合框选择已更改事件未触发

我在功能区栏中有一个组合框，如下所示：

<r:RibbonComboBox Label="Saved Queries" Name="Saved_Queries">
<r:RibbonGallery ScrollViewer.VerticalScrollBarVisibility="Auto"
  SelectionChanged="RibbonGallery_SelectionChanged">
<r:RibbonGallery.CategoryStyle>
<Style TargetType="{x:Type r:RibbonGalleryCategory}" 
  BasedOn="{StaticResource {x:Type r:RibbonGalleryCategory}}">
  <Setter Property="MinColumnCount" Value="1" />
  <Setter Property="MaxColumnCount" Value="1" />
  <Style.Triggers>
    <Trigger Property="Header" Value="Automatic Brush">
      <Setter Property="HeaderVisibility" Value="Collapsed" />
      <Setter Property="MinColumnCount" Value="1" />
      <Setter Property="MaxColumnCount" Value="1" />
      <Setter Property="IsSharedColumnSizeScope" Value="True" />
    </Trigger>
  </Style.Triggers>
</Style>
</r:RibbonGallery.CategoryStyle>
<r:RibbonGallery.GalleryItemTemplate>
  <DataTemplate>
    <Grid></Grid>
  </DataTemplate>
</r:RibbonGallery.GalleryItemTemplate>
<r:RibbonGalleryCategory >
</r:RibbonGalleryCategory>
</r:RibbonGallery>
</r:RibbonComboBox>

当在组合框中选择一个项目时，我正试图打开一个新窗口。但事实并非如此。我该怎么办